Positive electrode active material for nonaqueous electrolyte secondary battery

ABSTRACT

A positive electrode active material for a nonaqueous electrolyte secondary battery includes particles of a lithium-transition metal composite oxide that contains nickel in the composition thereof and has a layered structure. The particles have an average particle size D SEM  based on electron microscopic observation in a range of 1 μm to 7 μm in which a ratio D 50 /D SEM  of a 50% particle size D 50  in volume-based cumulative particle size distribution to the average particle size based on electron microscopic observation is in a range of 1 to 4, and a ratio D 90 /D 10  of a 90% particle size D 90  to a 10% particle size D 10  in volume-based cumulative particle size distribution is 4 or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.15/474,735, filed on Mar. 30, 2017, which claims priority to JapanesePatent Application No. 2016-072436, filed on Mar. 31, 2016, and JapanesePatent Application No. 2017-059661, filed on Mar. 24, 2017. All of theabove applications are hereby expressly incorporated by reference intothe present application.

BACKGROUND Field of the Invention

The present disclosure relates to a positive electrode active materialfor a nonaqueous electrolyte secondary battery.

Description of Related Art

A positive electrode active material for a nonaqueous electrolytesecondary battery for application to large-sized power machines, such aselectric vehicles, is required to have high output characteristics andhigh durability. In order to obtain high output characteristics, in apositive electrode active material having a structure in which a largenumber of primary particles are aggregated to form secondary particles,it is effective, for example, to have a hollow structure in eachsecondary particle to increase the BET specific surface area, and toreduce the size of aggregated primary particles of each secondaryparticle. However, in such a positive electrode active material, one ormore cracks may occur in the secondary particles due to pressurizationin the formation of an electrode, expansion/shrinkage upon charge anddischarge, etc., and there has been room for improvement in durability.

In relation to the above, a positive electrode active material in whichthe number of primary particles forming one secondary particle isreduced has been proposed (see, e.g., JP 2001-243949 A). In addition, apositive electrode active material in which primary particles aremonodispersed has been proposed (see, e.g., JP 2004-355824 A).

SUMMARY

A positive electrode active material for a nonaqueous electrolytesecondary battery includes particles of a lithium-transition metalcomposite oxide that contains nickel in the composition thereof and hasa layered structure. The particles have an average particle size D_(SEM)based on electron microscopic observation in a range of 1 μm to 7 μm, inwhich ratio D₅₀/D_(SEM) of a 50% particle size D₅₀ in volume-basedcumulative particle size distribution to the average particle size basedon electron microscopic observation is in a range of 1 to 4, and a ratioD₉₀/D₁₀ of a 90% particle size D₉₀ to a 10% particle size D₁₀ involume-based cumulative particle size distribution is 4 or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Example 1.

FIG. 2 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Example 3.

FIG. 3 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Example 4.

FIG. 4 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Example 5.

FIG. 5 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Example 6.

FIG. 6 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Comparative Example 1.

FIG. 7 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Comparative Example 2.

FIG. 8 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Example 7.

FIG. 9 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Example 8.

FIG. 10 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Comparative Example 3.

FIG. 11 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Comparative Example 4.

FIG. 12 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Example 10.

FIG. 13 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Example 11.

FIG. 14 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Example 12.

FIG. 15 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Comparative Example 5.

DETAILED DESCRIPTION

The present invention resides in a positive electrode active materialfor a nonaqueous electrolyte secondary battery with both high outputcharacteristics and high durability.

The invention is described in detail as follows, and includes theaspects shown below.

A first aspect is a positive electrode active material for a nonaqueouselectrolyte secondary battery, including particles of alithium-transition metal composite oxide that contains nickel in thecomposition thereof and has a layered structure, the particles having anaverage particle size D_(SEM) based on electron microscopic observationin a range of 1 μm to 7 μm, in which a ratio D₅₀/D_(SEM) of the 50%particle size D₅₀ in volume-based cumulative particle size distributionto the average particle size D_(SEM) is in a range of 1 to 4 based onelectron microscopic observation, and the ratio D₉₀/D₁₀ of the 90%particle size D₉₀ to the 10% particle size D₁₀ in volume-basedcumulative particle size distribution is 4 or less.

A second aspect is an electrode for a nonaqueous electrolyte secondarybattery, including a current collector and a positive electrode activematerial layer that is disposed on the current collector and containsthe positive electrode active material described above.

A third aspect is a nonaqueous electrolyte secondary battery includingthe electrode described above.

According to one embodiment of the present disclosure, a positiveelectrode active material for a nonaqueous electrolyte secondary batterycan be provided in which both high output power characteristics and highdurability can be achieved.

A positive electrode active material for a nonaqueous electrolytesecondary battery according the present disclosure will be described inthe description below based on embodiments. However, the followingembodiments are intended to embody the technical concept of the presentinvention, and the scope of the present invention is not limitedthereto. In the present specification, the content of each component ina composition refers to, in the case where a plurality of substancescorresponding to such a component are present in the composition, thetotal amount of the plurality of substances present in the compositionunless otherwise specified.

Positive Electrode Active Material for Nonaqueous Electrolyte SecondaryBattery

A positive electrode active material for a nonaqueous electrolytesecondary battery according to one embodiment of the present disclosure(hereinafter sometimes simply referred to as “positive electrode activematerial”) includes particles of a lithium-transition metal compositeoxide containing nickel in the composition thereof and having a layeredstructure. The particles have the average particle size D_(SEM) based onelectron microscopic observation in a range of 1 μm to 7 μm, in whichthe ratio D₅₀/D_(SEM) of the 50% particle size D₅₀ in volume-basedcumulative particle size distribution to the average particle size basedon electron microscopic observation is in a range of 1 to 4, and theratio D₉₀/D₁₀ of the 90% particle size D₉₀ to the 10% particle size D₁₀in volume-based cumulative particle size distribution is 4 or less.

The positive electrode active material contains lithium-transition metalcomposite oxide particles (hereinafter sometimes simply referred to as“composite oxide particles”) having the average particle size D_(SEM)based on electron microscopic observation in a range of 1 μm to 7 μm,the value of D₅₀/D_(SEM) in a range of 1 to 4, and the value of D₉₀/D₁₀of 4 or less. The value of D₅₀/D_(SEM) in a range of 1 to 4 indicatesthat the composite oxide particles are composed of a single primaryparticle or a small number of primary particles (hereinafter both maysimply referred to as “a single particle”), having reduced contact grainboundaries between primary particles. In addition, the value of D₉₀/D₁₀of 4 or less indicates that the composite oxide particles have a narrowdistribution width in volume-based cumulative particle sizedistribution, and the particle size is substantially uniform. With thesefeatures, high output characteristics and high durability can be bothachieved.

As compared with a positive electrode active material containinglithium-transition metal composite oxide particles having secondaryparticles made of a large number of aggregated primary particles, in aconventional positive electrode active material containinglithium-transition metal composite oxide particles, which are singleparticles, a decrease in capacity retention ratio due to thedisconnection of the electrical conduction path of lithium ions causedby the grain boundary dissociation of secondary particles during acharge/discharge cycle is prevented, and also an increase in thediffusion/migration resistance of lithium ions is prevented.Accordingly, good durability is exhibited. Meanwhile, in such aconventional positive electrode active material, a three-dimensionalgrain boundary network as in a positive electrode active material madeof aggregated particles is hardly formed, and a high-power designutilizing grain boundary conduction is difficult to achieve. Therefore,there has been a tendency that the output characteristics areinsufficient. It is believed that output power characteristics can beincreased by decreasing the particle size (D_(SEM)) of single particles.However, in the case where the particle size is too small, theinteraction between particles is increased, so that the electrode platefilling properties tend to be greatly deteriorated. Further, a decreasein powder fluidity may result in the handling ability being greatlydeteriorated. Meanwhile, in particular, for obtaining a practical energydensity, a certain degree of the particle size is needed. However, it isbelieved that an increase in particle size tends to result in a greaterlack of output power.

The lithium-transition metal composite oxide particles according to oneembodiment of the present disclosure have more uniform particle sizethan that of conventional single particles. With this configuration,even in the case where the battery is charged and discharged at a highcurrent density, variations in charge/discharge depth among particlesdue to current concentration on some particles can be reduced.Accordingly, it is believed that, while preventing increase inresistance due to current concentration, local degradation throughcharge/discharge cycles can be reduced.

Further, with uniform particle size of lithium-transition metalcomposite oxide particles having reduced grain boundaries, the particlesdo not collapse even when pressed at a high pressure in themanufacturing of an electrode. Accordingly, the space between particlesis considered to be homogenized. In addition, in the case where abattery is formed, the space between particles is filled with anelectrolyte to serve as a lithium ion diffusion path. With uniform sizeof such a diffusion path, variations in amount of charge/discharge amongparticles can be reduced. Accordingly, it is considered that, evenlithium-transition metal composite oxide particles having reducedcontact grain boundaries between primary particles can achieve goodoutput power characteristics while ensuring electrode plate fillingperformance.

Further, generally, in the case where single particles are synthesized,heat treatment is needed to be performed under high temperature forgrowth of particles. In particular, in a composition having a high Niproportion, when calcination is performed at a high temperature, theelement Ni may be incorporated into the Li site, that is, so-calleddisorder may occur. Disorder inhibits the diffusion of Li ions incomposite oxide particles and causes resistance, resulting in effectssuch as a decrease in charge/discharge capacity at a practical currentdensity, a decrease in output characteristics, etc. Therefore, it ispreferable that such disorder be suppressed. Suppressing disorder allowsfor further improving the capacity and output power characteristics insingle particles.

In the composite oxide particles forming the positive electrode activematerial, the average particle size Ds it based on electron microscopicobservation is in a range of 1 μm to 7 μm in view of durability. Theaverage particle size D_(SEM) based on electron microscopic observationis determined as follows. Using a scanning electron microscope (SEM),observation is performed at a magnification of 1,000 to 10,000 inaccordance with the particle size. One hundred particles havingrecognizable profiles are selected, and the equivalent sphericaldiameters of the selected particles are calculated using an imageprocessing software. The arithmetic average of the obtained equivalentspherical diameters is determined as D_(SEM).

In the composite oxide particles, the ratio D₅₀/D_(SEM) of the 50%particle size D₅₀ in volume-based cumulative particle size distributionto the average particle size D_(SEM) based on electron microscopicobservation is in a range of 1 to 4. In the case where D₅₀/D_(SEM) is 1,the composite oxide particles are single particles. In the case whereD₅₀/D_(SEM) is closer to 1, the composite oxide particles are made ofsmall number of primary particles. In view of durability, it ispreferable that D₅₀/D_(SEM) be in a range of 1 to 4. In view of poweroutput density, it is preferable that D₅₀/D_(SEM) be 3 or less,particularly preferably 2.5 or less.

Further, the 50% particle size D₅₀ of the composite oxide particles isin a range of 1 μm to 21 μm, for example. In view of power outputdensity, it is preferable that D₅₀ be 1.5 μm or more, more preferably 3μm or more, and be 8 μm or less, more preferably 5.5 μm or less.

The 50% particle size D₅₀ is determined as a particle size correspondingto a cumulative percentage of 50% from the smaller particle size side inthe volume-based cumulative particle size distribution measured underwet conditions using a laser diffraction particle size distributionanalyzer. Similarly, the 90% particle size D₉₀ and 10% particle size D₁₀described below are determined as particle sizes corresponding tocumulative percentages of 90% and 10%, respectively, from the smallerparticle size side.

In the composite oxide particles, the ratio of 90% particle size D₉₀ to10% particle size D₁₀ in volume-based cumulative particle sizedistribution indicates the width of particle size distribution. Thesmaller the value is, the more uniform the particle size. D₉₀/D₁₀ is 4or less. In view of power density, it is preferable that D₉₀/D₁₀ is 3 orless, more preferably 2.5 or less. The lower limit of Do/D₁₀ is 1.2 ormore, for example.

The lithium-transition metal composite oxide contains nickel in thecomposition thereof and has a layered structure. Examples of suchlithium-transition metal composite oxides include lithium-nickelcomposite oxides and lithium-nickel-cobalt-manganese composite oxides.Among them, a lithium-transition metal composite oxide preferably has acomposition represented by the following formula (1).

Li_(p)Ni_(x)Co_(y)M¹ _(z)O_(2+α)  (1)

In formula(1), p, x, y, z, and α satisfy 1.0≤p≤1.3, 0.3≤x≤0.95, 0≤y≤0.4,0≤z≤0.5, x+y+z=1, and −0.1≤α≤0.1, and M¹ represents at least one of Mnand Al.

The lithium-transition metal composite oxide particles may be doped withan element other than the elements forming the lithium-transition metalcomposite oxide. Examples of an element for doping include B, Na, Mg,Si, P, S, K, Ca, Ti, V, Cr, Zn, Sr, Y, Zr, Nb, Mo, In, Sn, Ba, La, Ce,Nd, Sm, Eu, Gd, Ta, W. and Bi. Examples of compounds used for dopingwith these elements include oxides and fluorides containing at least oneelement selected from the group consisting of these elements, and Licomposite oxides thereof. The amount of doping may be, for example,0.005 mol % or more and 10 mol % or less with respect to thelithium-transition metal composite oxide particles, for example.

The lithium-transition metal composite oxide particles may include coreparticles containing a lithium-transition metal composite oxide and adeposit disposed on the core particle surface. The deposit should bedisposed on at least a portion of the core particle surface, and ispreferably disposed in a region of 1% or more of the surface area of thecore particles. The composition of the deposit is suitably selected inaccordance with the purpose and the like, and examples thereof includeoxides and fluorides containing at least one kind selected from thegroup consisting of B, Na, Mg, Si, P. S, K, Ca, Ti, V. Cr, Zn, Sr, Y.Zr, Nb, Mo, In, Sn, Ba. La. Ce, Nd, Sm, Eu, Gd, Ta, W, and Bi, as wellas Li-composite oxides thereof. The content of deposit may be, forexample, in a range of 0.03 mass % to 10 mass %, preferably 0.1 mass %to 2 mass %, of the lithium-transition metal composite oxide particles.

The composition of lithium-transition metal composite oxide containsnickel. In the lithium-transition metal composite oxide, in view of theinitial efficiency in a nonaqueous electrolyte secondary battery, thedisorder of nickel element determined by X-ray diffractometry ispreferably 4.0% or less, more preferably 2.0% or less, and still morepreferably 1.5% or less. The expression “disorder of nickel element”refers to chemical disorder of nickel ions generated in a site oftransition metal ions. In a lithium-transition metal composite oxidehaving a layered structure, such a disorder is typically an exchangebetween lithium ions that occupies the site represented by 3 b whenexpressed in the Wyckoff symbol (i.e., 3b site, the same applieshereinafter) and transition metal ions that occupies the 3a site. Thesmaller disorder of nickel element is, the more initial efficiency isimproved, and thus is more preferable.

The disorder of elemental nickel in a lithium-transition metal compositeoxide can be determined by X-ray diffractometry. The X-ray diffractionspectrum of a lithium-transition metal composite oxide is measured usinga CuKα ray. The composition model is represented by Li_(1-d)Ni_(d)MeO₂(wherein Me is transition metals other than nickel in thelithium-transition metal composite oxide), and structural optimizationis performed by Rietveld analysis based on the obtained X-raydiffraction spectrum. The percentage of d calculated as a result ofstructural optimization is determined as the value of elemental nickeldisorder.

In the case where the lithium-transition metal composite oxide has acomposition represented by formula (1), in one embodiment of the presentinvention, the range of p, the ranges of particle sizes represented byD_(SEM), D₅₀, D₉₀, and D₁₀, and the preferred range of the disorder ofelemental nickel may vary in accordance with the value of x in formula(1). Examples thereof will be shown hereinafter.

In formula (1), in the case where x is within a range of 0.3≤x<0.6, inview of power density and electrode plate filling properties, it ispreferable that D_(SEM) be 1.1 μm or more, more preferably 1.3 μm ormore, and be 4 μm or less, more preferably 2 μm or less. In the casewhere x is within a range of 0.6≤x≤0.95, in view of power density andelectrode plate filling properties, it is preferable that D_(SEM) be 1.1μm or more, more preferably 1.3 μm or more, and be 5 μm or less, morepreferably 4 μm or less.

In formula (1), in the case where x satisfies 0.3≤x<0.8, in view ofpower density, it is preferable that D₅₀/D_(SEM) is in a range of 1 to2.

In formula (1), in the case where x satisfies 0.3≤x<0.6, in view ofpower density, it is preferable that at least one of the conditionsshown below be satisfied.

(i) In view of charge/discharge capacity, it is preferable that thedisorder of elemental nickel in the lithium-transition metal compositeoxide particles determined by X-ray diffractometry be 1.5% or less.

(ii) It is preferable that Do/D₁₀ be 3.0 or less, more preferably 2.5 orless.

(iii) In view of electrode plate filling properties, it is preferablethat D₅₀ be in a range of 1 μm to 5.5 μm, more preferably in a range of1 μm to 3 μm.

(iv) It is preferable that p in formula (1) satisfy 1.1<p<1.2.

In formula (1), in the case where x satisfies 0.6≤x<0.8, in view ofoutput power density, it is preferable that at least one of theconditions shown below be satisfied.

(i) In view of charge/discharge capacity, it is preferable that thedisorder of elemental nickel in the lithium-transition metal compositeoxide particles determined by X-ray diffractometry be 2.0% or less.

(ii) It is preferable that D₉₀/D₁₀ be 2.3 or less.

(iii) In view of electrode plate filling properties, it is preferablethat D₅₀ be in a range of 1 μm to 5.5 μm.

In formula (1), in the case where x satisfies 0.8≤x<0.95, in view ofpower density, it is preferable that at least one of the conditionsshown below be satisfied.

(i) In view of charge/discharge capacity, it is preferable that thedisorder of elemental nickel in the lithium-transition metal compositeoxide particles determined by X-ray diffractometry be 4.0% or less.

(ii) It is preferable that D₉₀/D₁₀ be 3.0 or less.

(iii) In view of electrode plate filling properties, it is preferablethat D₅₀ is in a range of 1 μm to 5.5 μm.

Method for Producing Positive Electrode Active Material

Lithium-transition metal composite oxide particles contained in thepositive electrode active material according to the present disclosurecan be produced by a method including: mixing a lithium compound and anoxide having a desired composition to obtain a raw material mixture; andsubjecting the obtained raw material mixture to a heat treatment. Theheat-treated product resulting from the heat treatment may be subjectedto a crushing treatment, and may further be subjected to a treatment forremoving unreacted substances, by-products, and the like by washing withwater, etc. The product may further be subjected to a dispersiontreatment, a classification treatment, and the like.

Examples of methods of obtaining an oxide having a desired compositioninclude: a method in which raw material compounds (hydroxide, carbonate,etc.) are mixed according to the intended composition and decomposedinto an oxide by a heat treatment; a coprecipitation method in which araw material compound soluble in a solvent is dissolved in a solvent,then control of the temperature, adjustment of the pH, or adding of acomplexing agent, for example, is performed to obtain a precipitate of aprecursor in accordance with the intended composition, and theprecursors are subjected to a heat treatment to obtain an oxide; and thelike.

An example of a method of producing a positive electrode active materialwill be described in the case where the lithium-transition metalcomposite oxide is represented by formula (1) shown below.

It is preferable that the method of obtaining a raw material mixtureincludes: providing a composite oxide containing nickel, cobalt, and atleast one of manganese and aluminum by a coprecipitation method; andmixing the obtained composite oxide with a lithium compound such aslithium carbonate or lithium hydroxide.

The method of obtaining a composite oxide by a coprecipitation methodcan include: a seed formation step of adjusting the pH and the like of amixed aqueous solution containing metal ions in a desired composition toobtain seed crystals; a crystallization step of growing the formed seedcrystals to obtain a composite hydroxide having desired characteristics;and a step of subjecting the obtained composite hydroxide to a heattreatment to obtain a composite oxide. The details of the method ofobtaining a composite oxide may be referred to in JP 2003-292322 A, JP2011-116580 A, and the like (the disclosures of which are incorporatedherein by reference in their entirety).

The composite oxide obtained by a coprecipitation method has a value ofD₉₀/D₁₀, which serves as an index of particle size distribution, of 3 orless, for example, preferably 2 or less. In addition, D₅₀ is 12 μm orless, for example, preferably 6 μm or less, and more preferably 4 μm orless, and is 1 μm or more, for example, preferably 2 μm or more.

The content ratio Ni/Co/(Mn+Al) of nickel, cobalt, andmanganese+aluminum in the composite oxide may be 1/1/1, 6/2/2, or 8/1/1,for example.

It is preferable that the raw material mixture contains a lithiumcompound in addition to the composite oxide. Examples of lithiumcompounds include lithium carbonate, lithium hydroxide, and lithiumoxide. The particle size of the lithium compound used is, as D₅₀, in arange of 0.1 μm to 100 μm, for example, preferably in a range of 2 μm to20 μm. The content of lithium with respect to the raw material mixturemay be, as Li/(Ni+Co+Mn+Al), 1.0 or more and 1.3 or less, for example,preferably 1.2 or less. The composite oxide and the lithium compound maybe mixed, for example, using a high-speed shear mixer or the like, forexample.

The obtained raw material mixture is subjected to a heat treatment,which allows for obtaining lithium-transition metal composite oxideparticles. The heat treatment is performed under a temperature in arange of 700° C. to 1,100° C., for example. The heat treatment may beperformed at a single temperature, or may also be performed at aplurality of temperatures. In the case where the heat treatment isperformed at a plurality of temperatures, for example, it is possible toperform a first heat treatment at a temperature in a range of 700° C. to925° C., and then perform a second heat treatment at a temperature in arange of 930° C. to 1,100° C. Further, a third heat treatment may beadditionally performed at a temperature in a range of 700° C. to 850° C.

The time of the heat treatment is in a range of 1 to 40 hours, forexample. In the case where the heat treatment is performed at aplurality of temperatures, each treatment may be performed for in arange of 1 to 10 hours. The heat treatment may be performed in the airor an oxygen atmosphere.

The heat-treated product may be subjected to a crushing treatment, adispersion treatment, a classification treatment, and the like. As aresult, desired lithium-transition metal composite oxide particles canbe obtained.

In addition, after being subjected to a crushing treatment, a dispersiontreatment, a classification treatment, or the like, the heat-treatedproduct may be further mixed with a lithium compound to obtain amixture, followed by an additional heat treatment. In the case where alithium compound is further mixed, the content of lithium in the mixturemay be, for example, represented as Li/(Ni+Co+Mn+Al), and may be in arange of 1.05 to 1.3, preferably 1.1 to 1.2. In addition, the additionalheat treatment may be performed at a temperature in a range of 850° C.to 1,000° C., preferably in a range of 870° C. to 950° C. It ispreferable that the temperature be lower than the temperature of theheat treatment of the raw material mixture. The heat treatment time ofthe additional heat treatment may be, for example in a range of 2 hoursto 15 hours. After the additional heat treatment, a crushing treatment,a dispersion treatment, a classification treatment, or the like may beperformed.

Electrode for Nonaqueous Electrolyte Secondary Battery

An electrode for a nonaqueous electrolyte secondary battery includes acurrent collector and a positive electrode active material layer that isdisposed on the current collector and contains the positive electrodeactive material for a nonaqueous electrolyte secondary battery describedabove. A nonaqueous electrolyte secondary battery including such anelectrode can achieve both high durability and high outputcharacteristics.

Examples of materials for the current collector include aluminum,nickel, and stainless steel. The positive electrode active materiallayer can be formed as below. A positive electrode mixture obtained bymixing the above positive electrode active material, an electricallyconductive material, a binder, and the like with a solvent is appliedonto a current collector, followed by a drying treatment, apressurization treatment, and the like. Examples of electricallyconductive materials include natural graphite, artificial graphite, andacetylene black. Examples of binders include polyvinylidene fluoride,polytetrafluoroethylene, and polyamide acrylic resin.

Nonaqueous Electrolyte Secondary Battery

A nonaqueous electrolyte secondary battery includes the electrode for anonaqueous electrolyte secondary battery described above. In addition tothe electrode for a nonaqueous electrolyte secondary battery, thenonaqueous electrolyte secondary battery further includes a negativeelectrode for a nonaqueous secondary battery, a nonaqueous electrolyte,a separator, and the like. As the negative electrode, nonaqueouselectrolyte, separator, and the like in the nonaqueous electrolytesecondary battery, those for a nonaqueous electrolyte secondary batterydescribed in JP 2002-075367 A, JP 2011-146390 A, JP 2006-12433 A. andthe like (the disclosures of which are incorporated herein by referencein their entirety) may be suitably used, for example.

EXAMPLES

Examples of the present invention will be described below in detail.

First, methods of measuring physical properties in examples andcomparative examples in the below will be described.

The value of D₁₀, D₅₀, and D₉₀ were determined by, with use of a laserdiffraction particle size distribution analyzer (SALD-3100 manufacturedby Shimadzu Corporation), measuring volume-based cumulative particlesize distribution, and calculating the value of each of D₁₀, D₅₀, andD₉₀ corresponding to the respective cumulative percentages from thesmaller particle size side were determined.

The average particle size D_(SEM) based on electron microscopicobservation was determined as follows. In an image observed at amagnification of 1,000 to 10,000 using a scanning electron microscope(SEM), 100 particles having recognizable outlines were selected, and theequivalent spherical diameters of the selected particles were calculatedusing an image processing software (Image J).

The arithmetic average of the obtained equivalent spherical diameterswas determined as D_(SEM).

The value of elemental nickel disorder (amount of Ni disorder) wasdetermined by X-ray diffractometry as below.

The X-ray diffraction spectrum of obtained lithium-transition metalcomposite oxide particles was measured using a CuKα ray under conditionsof a tube current of 40 mA and a tube voltage of 40 kV With thecomposition model being expressed as Li_(1-d)Ni_(d)MeO₂ (wherein Me istransition metals other than nickel in the lithium-transition metalcomposite oxide), based on the obtained X-ray diffraction spectrum, thestructure of the lithium-transition metal composite oxide particles wasoptimized by Rietveld analysis using RIETAN-2000 software. Thepercentage of d calculated as a result of structural optimization wasdetermined as the amount of Ni disorder.

Example 1 Seed Formation Step

First, 10 kg of water was charged in a reaction tank, an aqueous ammoniasolution was added into water while stirring water, and the ammonium ionconcentration was adjusted to 1.8 mass %. The temperature in the tankwas set at 25° C., and a nitrogen gas was circulated in the tank tomaintain the oxygen concentration of the inner space of the reactiontank at 10 vol % or less. A 25 mass % aqueous sodium hydroxide solutionwas added to water in the reaction tank, and the pH value of thesolution in the tank was adjusted to 13.5 or more.

Next, a nickel sulfate solution, a cobalt sulfate solution, and amanganese sulfate solution were mixed to prepare a mixed aqueoussolution having a molar ratio of 1:1:1.

The mixed aqueous solution was added to the solution in the reactiontank until the solute content reached 4 mol, and, while controlling thepH value of the reaction solution at 12.0 or more with a sodiumhydroxide solution, seed formation was performed.

Crystallization Step

After the seed formation step, the temperature in the tank wasmaintained at 25° C. or more until the completion of the crystallizationstep. In addition, a mixed aqueous solution having a solute content of1,200 mol was prepared and added to the reaction tank simultaneouslywith an aqueous ammonia solution while maintaining the ammonium ionconcentration in the solution at 2,000 ppm or more over 5 hours or moreso that no additional seed formation would take place in the reactiontank. During the reaction, the pH value of the reaction solution wascontrolled to be maintained in a range of 10.5 to 12.0 with a sodiumhydroxide solution. Sampling was successively performed during thereaction, and the addition was completed when the D₅₀ of the compositehydroxide particles reached about 4.5 μm.

Next, the product was washed with water, filtered, and dried, so thatcomposite hydroxide particles are obtained. The obtained hydroxideprecursor was subjected to a heat treatment at 300° C. for 20 hours inthe ambient atmosphere, thereby obtaining a composite oxide having thefollowing properties: composition ratio Ni/Co/Mn=0.33/0.33/0.33, D₁₀=3.4μm, D₅₀=4.5 μm, D₉₀=6.0 μm, D₉₀/D₁₀=1.8.

Synthesis Step

The obtained composite oxide and lithium carbonate were mixed so thatLi/(Ni+Co+Mn) becomes 1.15 to obtain a raw material mixture. Theobtained raw material mixture was calcined in air at 925° C. for 7.5hours and then calcined at 1,030° C. for 6 hours to obtain a sinteredbody. The obtained sintered body was crushed, subjected to a dispersiontreatment in a ball mill made of resin for 10 minutes, and thendry-sieved to obtain a powder. The obtained powder was classifiedthrough a dry classifier into three sizes (large, medium, and small),and medium-sized particles were collected. The proportion ofmedium-sized particles after classification relative to beforeclassification was 46 wt %.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.15)Ni_(0.33)Co_(0.33)Mn_(0.33)O₂ and having the followingproperties were obtained: average particle size D_(SEM) based onelectron microscopic observation: 3.6 μm, D₁₀=3.7 μm, D₅₀=5.1 μm,D₉₀=6.7 μm, ratio D₅₀/D_(SEM) of D₅₀ to average particle size D_(SEM):1.4, ratio D₉₀/D₁₀ in particle size distribution: 1.8, amount of Nidisorder: 0.3%. The physical property values of the obtainedlithium-transition metal composite oxide particles are shown in Table 1,and an SEM image thereof is shown in FIG. 1.

Example 2

Under the same conditions as in Example 1 except that the timing of thecompletion of addition of a mixed aqueous solution in thecrystallization step was changed to the time where the value of D₅₀ ofcomposite hydroxide particles reached about 3.0 μm, a composite oxidehaving the following properties was obtained: composition ratioNi/Co/Mn=0.33/0.33/0.33, D₁₀=2.2 μm, D₅₀=3.0 μm, D₉₀=4.1 μm,D₉₀/D₁₀=1.9. The obtained composite oxide and lithium carbonate weremixed so that Li/(Ni+Co+Mn) becomes 1.05 to obtain a raw materialmixture. The obtained raw material mixture was calcined in air at 925°C. for 7.5 hours and then calcined at 1,030° C. for 6 hours to obtain asintered body. The obtained sintered body was crushed, subjected to adispersion treatment in a ball mill made of resin for 30 minutes, andthen dry-sieved to obtain a powder. The obtained powder and lithiumcarbonate were mixed so that Li/(Ni+Co+Mn) becomes 1.17 and calcined inair at 700° C. for 10 hours to obtain a sintered body. The obtainedsintered body was crushed, subjected to a dispersion treatment in a ballmill made of resin for 30 minutes, and then dry-sieved to obtain powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.17)Ni_(0.33)Co_(0.33)Mn_(0.33)O₂ and having the followingproperties were obtained: average particle size D_(SEM): 1.2 μm, D₁₀=1.4μm, D₅₀=3.2 μm, D₉₀=5.1 μm, ratio D₅₀/D_(SEM) of D₅₀ to average particlesize D_(SEM): 2.7, ratio D₉₀/D₁₀ in particle size distribution: 3.6,amount of Ni disorder: 1.7%. The physical property values of theobtained lithium-transition metal composite oxide particles are shown inTable 1.

Example 3

A composite oxide was obtained under the same conditions as in Example2. The obtained composite oxide and lithium carbonate were mixed so thatLi/(Ni+Co+Mn) becomes 1.05 to obtain a raw material mixture. Theobtained raw material mixture was calcined in air at 925° C. for 7.5hours and then calcined at 1,030° C. for 6 hours to obtain a sinteredbody. The obtained sintered body was crushed, subjected to a dispersiontreatment in a ball mill made of resin for 30 minutes, and thendry-sieved to provide powder. The obtained powder and lithium carbonatewere mixed so that Li/(Ni+Co+Mn) becomes 1.17 and calcined in air at900° C. for 10 hours to obtain a sintered body. The obtained sinteredbody was crushed, subjected to a dispersion treatment in a ball millmade of resin for 30 minutes, and then dry-sieved to give a powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.17)Ni_(0.33)Co_(0.33)Mn_(0.33)O₂ and having the followingproperties were obtained: average particle size D_(SEM): 1.2 μm, D₁₀=1.5μm, D₅₀=3.3 μm, D₉₀=5.1 μm, ratio D₅₀/D_(SEM) of D₅₀ to average particlesize D_(SEM): 2.8, ratio D₉₀/D₁₀ in particle size distribution: 3.4,amount of Ni disorder: 0.9%. The physical property values of theobtained lithium-transition metal composite oxide particles are shown inTable 1, and an SEM image thereof is shown in FIG. 2.

Example 4

A composite oxide was obtained under the same conditions as in Example2. The obtained composite oxide and lithium carbonate were mixed so thatLi/(Ni+Co+Mn) becomes 1.05 to obtain a raw material mixture. Theobtained raw material mixture was calcined in air at 925° C. for 7.5hours and then calcined at 1,030° C. for 6 hours to obtain a sinteredbody. The obtained sintered body was crushed, subjected to a dispersiontreatment in a ball mill made of resin for 30 minutes, and thendry-sieved to obtain a powder. The obtained powder and lithium carbonatewere mixed so that Li/(Ni+Co+Mn) becomes 1.17 and calcined in air at900° C. for 10 hours to give a sintered body. The obtained sintered bodywas crushed, subjected to a dispersion treatment twice using a jet millwith the feed pressure adjusted to 0.4 MPa and the grinding pressureadjusted to 0.55 MPa so as to prevent the primary particles from beingground, and then dry-sieved to give a powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.17)Ni_(0.33)Co_(0.33)Mn_(0.33)O₂ and having the followingproperties were obtained: average particle size D_(SEM): 1.4 μm. D₁₀=1.1μm, D₅₀=1.9 μm, D₉₀=2.8 μm, ratio D₅₀/D_(SEM) of D₅₀ to average particlesize D_(SEM): 1.4, ratio D₉₀/D₁₀ in particle size distribution: 2.5,amount of Ni disorder: 1.0%. The physical property values of theobtained lithium-transition metal composite oxide particles are shown inTable 1, and an SEM image thereof is shown in FIG. 3.

Example 5

Under the same conditions as in Example 1 except that the timing of thecompletion of addition of a mixed aqueous solution in thecrystallization step was changed to the time where the D₅₀ of compositehydroxide particles reached 9.9 μm, a composite oxide having thefollowing properties was obtained: composition ratioNi/Co/Mn=0.33/0.33/0.33, D₁₀=8.6 μm, D₅₀=9.9 μm, D₉₀=12.7 μm,D₉₀/D₁₀=1.5. The obtained composite oxide and lithium carbonate weremixed so that Li/(Ni+Co+Mn) becomes 1.05 to obtain a raw materialmixture. The obtained raw material mixture was calcined in air at 925°C. for 7.5 hours and then calcined at 1,080° C. for 6 hours to obtain asintered body. The obtained sintered body was crushed, subjected to adispersion treatment in a ball mill made of resin for 10 minutes, andthen dry-sieved to obtain a powder. The obtained powder and lithiumcarbonate were mixed so that Li/(Ni+Co+Mn) becomes 1.14 and calcined inair at 900° C. for 10 hours to obtain sintered body. The obtainedsintered body was crushed, subjected to a dispersion treatment in a ballmill made of resin for 10 minutes, and then dry-sieved to obtain powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.14)Ni_(0.33)Co_(0.33)Mn_(0.33)O₂ and having the followingproperties were obtained: average particle size D_(SEM): 6.8 μm, D₁₀=7.6μm, D₅₀=10.4 μm, D₉₀=16.4 nm, ratio D₅₀/D_(SEM) of D₅₀ to averageparticle size D_(SEM): 1.5, ratio D₉₀/D₁₀ in particle size distribution:2.2, amount of Ni disorder: 1.1%. The physical property values of theobtained lithium-transition metal composite oxide particles are shown inTable 1, and an SEM image thereof is shown in FIG. 4.

Example 6

A composite oxide was obtained under the same conditions as in Example2. The obtained composite oxide and lithium carbonate were mixed so thatLi/(Ni+Co+Mn) becomes 1.05 to obtain a raw material mixture. Theobtained raw material mixture was calcined in air at 925° C. for 7.5hours and then calcined at 1,030° C. for 6 hours to obtain a sinteredbody. The obtained sintered body was crushed, subjected to a dispersiontreatment in a ball mill made of resin for 10 minutes, and thendry-sieved to obtain a powder. The obtained powder and lithium carbonatewere mixed so that Li/(Ni+Co+Mn) becomes 1.14 and calcined in air at900° C. for 10 hours to obtain a sintered body. The obtained sinteredbody was crushed, subjected to a dispersion treatment in a ball millmade of resin for 10 minutes, and then dry-sieved to obtain a powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.14)Ni_(0.33)Co_(0.33)Mn_(0.33)O₂ and having the followingproperties were obtained: average particle size D_(SEM): 1.25 μm,D₁₀=2.7 μm, D₅₀=4.5 μm, D₉₀=6.7 μm, ratio D₅₀/D_(SEM) of D₅₀ to averageparticle size D_(SEM) of primary particles: 3.6, ratio D₉₀/D₁₀ inparticle size distribution: 2.5, amount of Ni disorder: 1.0%. Thephysical property values of the obtained lithium-transition metalcomposite oxide particles are shown in Table 1, and an SEM image thereofis shown in FIG. 5.

Comparative Example 1

Under the same conditions as in Example 1 except that, during thereaction in the crystallization step, a seed slurry prepared in the seedformation step to the reaction tank was added several times, and thetiming of the completion of addition of a mixed aqueous solution waschanged to the time at which the D₅₀ of composite hydroxide particlesreached 5.0 μm, a composite oxide having the following properties wasobtained: composition ratio Ni/Co/Mn=0.33/0.33/0.33, D₁₀=2.4 μm, D₅₀=5.0μm, D₉₀=12.2 μm, D₉₀/D₁₀=5.1. The obtained composite oxide and lithiumcarbonate were mixed so that Li/(Ni+Co+Mn) becomes 1.05 to obtain a rawmaterial mixture. The obtained raw material mixture was calcined in airat 925° C. for 7.5 hours and then calcined at 1,030° C. for 6 hours toobtain a sintered body. The obtained sintered body was crushed,subjected to a dispersion treatment in a ball mill made of resin for 10minutes, and then dry-sieved to obtain powder. The obtained powder andlithium carbonate were mixed so that Li/(Ni+Co+Mn) becomes 1.14 andcalcined in air at 900° C. for 10 hours to obtain a sintered body. Theobtained sintered body was crushed, subjected to a dispersion treatmentin a ball mill made of resin for 10 minutes, and then dry-sieved toobtain powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.14)Ni_(0.33)Co_(0.33)Mn_(0.33)O₂ and having the followingproperties were obtained: average particle size D_(SEM): 3.65 μm,D₁₀=2.5 μm, D₅₀=7.0 μm, D₉₀=13.5 μm, ratio D₅₀/D_(SEM) of D₅₀ to averageparticle size of primary particles: 1.9, ratio D₉₀/D₁₀ in particle sizedistribution: 5.4, amount of Ni disorder: 0.9%. The physical propertyvalues of the obtained lithium-transition metal composite oxideparticles are shown in Table 1, and an SEM image thereof is shown inFIG. 6.

Comparative Example 2

A composite oxide was obtained under the same conditions as in Example2. The obtained composite oxide and lithium carbonate were mixed so thatLi/(Ni+Co+Mn) becomes 1.15 to obtain a raw material mixture. Theobtained raw material mixture was calcined in air at 950° C. for 15hours to obtain a sintered body. The obtained sintered body was crushed,subjected to a dispersion treatment in a ball mill made of resin for 10minutes, and then dry-sieved to obtain a powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.15)Ni_(0.33)Co_(0.33)Mn_(0.33)O₂ and having the followingproperties were obtained: average particle size D_(SEM): 0.49 μm,D₁₀=3.0 μm, D₅₀=4.4 μm, D₉₀=7.6 μm, D₅₀/D_(SEM), a ratio of D₅₀ toaverage particle size D_(SEM): 9.0, D₉₀/D₁₀ in particle sizedistribution: 2.5, amount of Ni disorder: 0.9%. The physical propertyvalues of the obtained lithium-transition metal composite oxideparticles are shown in Table 1, and an SEM image thereof is shown inFIG. 7.

Example 7

Under the same conditions as in Example 1, except that the molar ratioof the nickel sulfate solution, cobalt sulfate solution, and manganesesulfate solution in the mixed aqueous solution were changed to 6:2:2,and that the timing of the completion of addition of the mixed aqueoussolution in the crystallization step was changed to the time at whichthe D₅₀ of the composite hydroxide particles reached 4.7 μm, a compositeoxide having the following properties was obtained: composition ratioNi/Co/Mn=0.60/0.20/0.20, D₁₀=4.0 μm, D₅₀=4.7 μm, D₉₀=6.2 μm.D₉₀/D₁₀=1.6. The obtained composite oxide and lithium hydroxidemonohydrate were mixed so that Li/(Ni+Co+Mn) becomes 1.06 to obtain araw material mixture. The obtained raw material mixture was calcined inan oxygen stream at 870° C. for 7 hours and then calcined at 970° C. for7 hours to obtain a sintered body. The obtained sintered body wascrushed and subjected to a dispersion treatment in a ball mill made ofresin for 10 minutes to obtain a powder. Further, the powder and 10 mass% of water with respect to the powder were added to a high-speedstirring mixer equipped with a rotating blade. he mixture was stirred at2,000 rpm to elute the residual alkali from the grain boundaries andperform a dispersion treatment, dried at 350° C., and then dry-sieved toobtain a powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.06)Ni_(0.60)Co_(0.20)Mn_(0.20)O₂ and having the followingproperties were obtained: average particle size D_(SEM): 3.7 μm, D₁₀=3.4μm, D₅₀=5.4 μm, D₉₀=7.7 μm, ratio D₅₀/D_(SEM) of D₅₀ to average particlesize D_(SEM): 1.5, ratio D₉₀/D₁₀ in particle size distribution: 2.3,amount of Ni disorder: 1.5%. The physical property values of theobtained lithium-transition metal composite oxide particles are shown inTable 1, and an SEM image thereof is shown in FIG. 8.

Example 8

A composite oxide was obtained under the same conditions as in Example7. The obtained composite oxide and lithium hydroxide monohydrate weremixed so that Li/(Ni+Co+Mn) becomes 1.17 to obtain a raw materialmixture. The obtained raw material mixture was calcined in air at 930°C. for 10 hours to obtain a sintered body. The obtained sintered bodywas crushed and subjected to a dispersion treatment in a ball mill madeof resin for 10 minutes to obtain a powder. Further, the powder and 10mass % of water relative to the powder were added to a high-speedstirring mixer equipped with a rotating blade. The mixture was stirredat 2,000 rpm to elute the residual alkali from the grain boundaries andperform a dispersion treatment, dried at 350° C., and then dry-sieved toobtain a powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.17)Ni_(0.60)Co_(0.20)Mn_(0.20)O₂ and having the followingproperties were obtained: average particle size D_(SEM): 3.2 μm, D₁₀=3.6μm, D₅₀=6.1 μm. D₉₀=9.2 μm, ratio D₅₀/D_(SEM) of D₅₀ to average particlesize D_(SEM): 1.9, ratio D₉₀/D₁₀ in particle size distribution: 2.6,amount of Ni disorder: 1.2%. The physical property values of theobtained lithium-transition metal composite oxide particles are shown inTable 1, and an SEM image thereof is shown in FIG. 9.

Example 9

A composite oxide was obtained under the same conditions as in Example7. The obtained composite oxide and lithium carbonate were mixed so thatLi/(Ni+Co+Mn) becomes 1.17 to obtain a raw material mixture. Theobtained raw material mixture was calcined in air at 930° C. for 10hours to obtain a sintered body. The obtained sintered body was crushedand subjected to a dispersion treatment in a ball mill made of resin for10 minutes to obtain a powder. Further, the powder and 10 mass % ofwater with respect to the powder were added to a high-speed stirringmixer equipped with a rotating blade. The mixture was stirred at 2,000rpm to elute the residual alkali from the grain boundaries and perform adispersion treatment, dried at 350° C., and then dry-sieved to obtainpowder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.17)Ni_(0.60)Co_(0.20)Mn_(0.20)O₂ and having the followingproperties were obtained: average particle size D_(SEM): 3.1 μm, D₁₀=3.8μm, D₅₀=6.3 μm, D₉₀=9.6 μm, ratio D₅₀/D_(SEM) of D₅₀ to average particlesize D_(SEM): 2.0, ratio D₉₀/D₁₀ in particle size distribution: 2.5,amount of Ni disorder: 2.2%. The physical property values of theobtained lithium-transition metal composite oxide particles are shown inTable 1.

Comparative Example 3

A composite oxide was obtained under the same conditions as in Example7. The obtained composite oxide and lithium hydroxide monohydrate weremixed so that Li/(Ni+Co+Mn) becomes 1.17 to obtain a raw materialmixture. The obtained raw material mixture was calcined in air at 810°C. for 10 hours to obtain a sintered body. The obtained sintered bodywas crushed, subjected to a dispersion treatment in a ball mill made ofresin for 10 minutes, and then dry-sieved to obtain a powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.17)Ni_(0.60)Co_(0.20)Mn_(0.20)O₂ and having the followingproperties were obtained: average particle size D_(SEM): 0.4 μm, D₁₀=3.2μm, D₅₀=4.7 μm, D₉₀=7.5 μm, ratio D₅₀/D_(SEM) of D₅₀ to average particlesize D_(SEM) of primary particles: 11.8, ratio D₉₀/D₁₀ in particle sizedistribution: 2.3, amount of Ni disorder: 1.0%. The physical propertyvalues of the obtained lithium-transition metal composite oxideparticles are shown in Table 1, and an SEM image thereof is shown inFIG. 10.

Comparative Example 4

A composite oxide was obtained under the same conditions as in Example7. The obtained composite oxide and lithium hydroxide monohydrate weremixed so that Li/(Ni+Co+Mn) becomes 1.17 to obtain a raw materialmixture. The obtained raw material mixture was calcined in air at 930°C. for 10 hours to give a sintered body. The obtained sintered body wascrushed, subjected to a dispersion treatment in a ball mill made ofresin for 10 minutes, and then dry-sieved to obtain a powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.17)Ni_(0.60)Co_(0.20)Mn_(0.20)O₂ and having the followingproperties were obtained: average particle size D_(SEM): 3.2 μm, D₁₀=4.1μm, D₅₀=9.6 μm, D₉₀=23.4 μm, ratio D₅₀/D_(SEM) of D₅₀ to averageparticle size D_(SEM): 3.0, ratio D₉₀/D₁₀ in particle size distribution:5.7, amount of Ni disorder: 1.3%. The physical property values of theobtained lithium-transition metal composite oxide particles are shown inTable 1, and an SEM image thereof is shown in FIG. 11.

Example 10

Under the same conditions as in Example 1, except that the mixing ratioof a nickel sulfate solution, a cobalt sulfate solution, and a manganesesulfate solution was changed to a molar ratio of 8:1:1 to obtain a mixedaqueous solution, and that the timing of the completion of addition ofthe mixed aqueous solution in the crystallization step was changed tothe time at which the D₅₀ of composite hydroxide particles reached 4.7μm, a composite oxide having the following properties was obtained:composition ratio Ni/Co/Mn=0.80/0.10/0.10, D₁₀=3.4 μm, D₅₀=4.6 μm,D₉₀=6.1 μm, D₉₀/D₁₀=1.8. The obtained composite oxide and lithiumhydroxide monohydrate were mixed so that Li/(Ni+Co+Mn) becomes 1.04 toobtain a raw material mixture. The obtained raw material mixture wascalcined in an oxygen stream at 780° C. for 5 hours, then calcined at1,000° C. for 10 hours, and further calcined at 780° C. for 5 hours toobtain a sintered body. The obtained sintered body was crushed andsubjected to a dispersion treatment in a ball mill made of resin for 10minutes to obtain a powder. Further, the powder and 10 mass % of waterwith respect to the powder were added to a high-speed stirring mixerequipped with a rotating blade. The mixture was stirred at 2,000 rpm toelute the residual alkali from the grain boundaries and perform adispersion treatment, dried at 350° C., and then dry-sieved to obtain apowder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.04)Ni_(0.80)Co_(0.10)Mn_(0.10)O₂ and having the followingproperties were obtained: average particle size D_(SEM): 3.1 μm, D₁₀=3.7μm, D₅₀=7.1 μm, D₉₀=12.0 μm ratio D₅₀/D_(SEM) of D₅₀ to average particlesize D_(SEM): 2.3, ratio D₉₀/D₁₀ in particle size distribution: 3.2,amount of Ni disorder: 1.7%. The physical property values of theobtained lithium-transition metal composite oxide particles are shown inTable 1, and an SEM image thereof is shown in FIG. 12.

Example 11

A composite oxide was obtained under the same conditions as in Example10. The obtained composite oxide and lithium hydroxide monohydrate weremixed so that Li/(Ni+Co+Mn) becomes 1.04 to obtain a raw materialmixture. The obtained raw material mixture was calcined in an oxygenstream at 780° C. for 5 hours and then calcined at 950° C. for 10 hoursto obtain a sintered body. The obtained sintered body was crushed andsubjected to a dispersion treatment in a ball mill made of resin for 10minutes to obtain a powder. Further, the powder and 10 mass % of waterwith respect to the powder were added to a high-speed stirring mixerequipped with a rotating blade. he mixture was stirred at 2,000 rpm toelute the residual alkali from the grain boundaries and perform adispersion treatment, dried at 350° C. and then dry-sieved to obtain apowder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.04)Ni_(0.80)Co_(0.10)Mn_(0.10)O₂ and having the followingproperties were obtained: average particle size D_(SEM): 2.5 μm, D₁₀=3.0μm, D₅₀=5.3 μm, D₉₀=8.2 μm, ratio D₅₀/D_(SEM) of D₅₀ to average particlesize D_(SEM): 2.1, ratio D₉₀/D₁₀ in particle size distribution: 2.7,amount of Ni disorder: 2.3%. The physical property values of theobtained lithium-transition metal composite oxide particles are shown inTable 1, and an SEM image thereof is shown in FIG. 13.

Example 12

A composite oxide was obtained under the same conditions as in Example10. The obtained composite oxide and lithium hydroxide monohydrate weremixed so that Li/(Ni+Co+Mn) becomes 1.04 to obtain a raw materialmixture. The obtained raw material mixture was calcined in an oxygenstream at 780° C. for 5 hours and then calcined at 1,000° C. for 10hours to give a sintered body. The obtained sintered body was crushedand subjected to a dispersion treatment in a ball mill made of resin for10 minutes to obtain a powder. Further, the powder and 10 mass % ofwater with respect to the powder were added to a high-speed stirringmixer equipped with a rotating blade. The mixture was stirred at 2,000rpm to elute the residual alkali from the grain boundaries and perform adispersion treatment, dried at 350° C., and then dry-sieved to obtain apowder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.04)Ni_(0.80)Co_(0.10)Mn_(0.10)O₂ and having the followingproperties were obtained: average particle size D_(SEM): 3.0 μm, D₁₀=3.7μm, D₅₀=6.6 μm, D₉₀=9.6 μm, ratio D₅₀/D_(SEM) of D₅₀ to average particlesize D_(SEM): 2.2, ratio D₉₀/D₁₀ in particle size distribution: 2.6,amount of Ni disorder: 4.2%. The physical property values of theobtained lithium-transition metal composite oxide particles are shown inTable 1, and an SEM image thereof is shown in FIG. 14.

Comparative Example 5

Under the same conditions as in Example 1, except that the mixed aqueoussolution was changed to a mixture of a nickel sulfate solution and acobalt sulfate solution mixed at molar ratio of 80:15, and that thetiming of the completion of addition of the mixed solution in thecrystallization step was changed to the time at which the D₅₀ ofcomposite hydroxide particles reached 4.6 μm, a composite oxide havingthe following properties was obtained: composition ratioNi/Co=0.80/0.15, D₁₀=3.4 μm, D₅₀=4.6 μm, D₉₀=6.1 μm, D₉₀/D₁₀=1.8. Theobtained composite oxide and aluminum oxide were mixed so thatcomposition ratio of Ni/Co/Al becomes 0.80/0.15/0.05, and lithiumhydroxide monohydrate was mixed so that Li/(Ni+Co+Al) becomes 1.04, sothat a raw material mixture is obtained. The obtained raw materialmixture was calcined in air at 710° C. for 5 hours to obtain a sinteredbody. The obtained sintered body was crushed, subjected to a dispersiontreatment in a ball mill made of resin for 10 minutes, and thendry-sieved to obtain a powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.04)Ni_(0.80)Co_(0.15)MnAl_(0.05)O₂ and having the followingproperties were obtained: average particle size D_(SEM): 0.3 μm, D₁₀=4.5μm, D₅₀=5.8 μm, D₉₀=7.4 μm, ratio D₅₀/D_(SEM) of D₅₀ to average particlesize D_(SEM): 19.3, ratio D₉₀/D₁₀ in particle size distribution: 1.6,amount of Ni disorder: 1.0%. The physical property values of theobtained lithium-transition metal composite oxide particles are shown inTable 1, and an SEM image thereof is shown in FIG. 15.

Evaluation

Using the lithium-transition metal composite oxides obtained above aspositive electrode active materials, batteries for evaluation wereproduced as below.

Production of Positive Electrode

Ninety six parts by mass of a positive electrode active material, 3parts by mass of acetylene black, and 1 part by mass of polyvinylidenefluoride (PVDF) were dispersed in N-methyl-2-pyrrolidone (NMP) toprepare a positive electrode mixture. The obtained positive electrodemixture was applied to an aluminum foil that serves as a currentcollector, dried, then compression-molded using a roll press, and cutinto a predetermined size, so that a positive electrode was produced.

Production of Negative Electrode

Ninety six parts by mass of a negative electrode active material and 4parts by mass of PVDF were dispersed in NMP to prepare a negativeelectrode mixture. The obtained negative electrode mixture was appliedto a copper foil as a current collector, dried, then compression-moldedusing a roll press, and cut into a predetermined size, so that anegative electrode was produced.

Production of Battery for Evaluation

Lead electrodes were attached to the positive electrode currentcollector and the negative electrode current collector, respectively,then a separator was placed between the positive electrode and thenegative electrode, and they were housed in a bag-shaped laminate pack.Next, the laminate pack was vacuum-dried at 65° C. to remove themoisture adsorbed on each member. Subsequently, in an argon atmosphere,an electrolyte solution was injected into the laminate pack and sealed.The battery thus obtained was placed in a thermostat at 25° C. and agedunder a weak current. For the electrolyte solution, a solution preparedby mixing ethylene carbonate (EC) and methylethyl carbonate (MEC) at avolume ratio of 3:7, and then dissolving lithium hexafluorophosphate(LiPF₆) to a concentration of 1 mol/l, was used.

Charge/Discharge Test

With respect to the batteries for evaluation obtained above, the powerdensity and durability were evaluated as below.

Power Density

A battery for evaluation was discharged to 50% SOC and maintained underan environment at 25° C. for 2 hours. Subsequently, from the state wherethe SOC is 50%, the battery was discharged at a constant current, the DCresistance after 10 seconds was measured, and the power density wascalculated. The minimum discharge voltage was set at 2.7 V.

Durability

A charge/discharge cycle test was performed under a temperaturecondition of 60° C. In the charge/discharge cycle test, as one cycle, abattery was charged at a constant current having a current density of2.0 mA/cm² to the maximum charge voltage of 4.2 V and then discharged ata constant current having a current density of 2.0 mA/cm² to the minimumdischarge voltage of 2.7 V. This cycle was repeated 1.000 times intotal. Then, the discharge capacity was measured in each cycle, anddurability (%) was calculated using the following formula: (dischargecapacity in the 1,000th cycle/discharge capacity in the firstcycle)×100. The evaluation results are shown in Table 1.

TABLE 1 amount of Power Comosition D_(SEM) D₁₀ D₅₀ D₉₀ Ni DisorderDensity Durability p x y z (μm) (μm) (μm) (μm) D₅₀/D_(SEM) D₉₀/D₁₀ (%)(W/kg) (%) Example 1 1.15 0.33 0.33 0.33 3.6 3.7 5.1 6.7 1.4 1.8 0.39560 86 Example 2 1.17 0.33 0.33 0.33 1.2 1.4 3.2 5.1 2.7 3.6 1.7 780086 Example 3 1.17 0.33 0.33 0.33 1.2 1.5 3.3 5.1 2.8 3.4 0.9 8090 85Example 4 1.17 0.33 0.33 0.33 1.4 1.1 1.9 2.8 1.4 2.5 1.0 10220 86Example 5 1.14 0.33 0.33 0.33 6.8 7.6 10.4 16.4 1.5 2.2 1.1 9180 86Example 6 1.14 0.33 0.33 0.33 1.25 2.7 4.5 6.7 3.8 2.5 1.0 6810 76Comparative 1.14 0.33 0.33 0.33 3.65 2.5 7 13.5 1.9 5.4 0.9 6200 76Example 1 Comparative 1.15 0.33 0.33 0.33 0.49 3 4.4 7.6 9.0 2.5 0.95950 78 Example 2 Example 7 1.06 0.6 0.2 0.2 3.7 3.4 5.4 7.7 1.5 2.3 1.510500 84 Example 8 1.17 0.6 0.2 0.2 3.2 3.6 6.1 9.2 1.9 2.6 1.2 9800 85Example 9 1.17 0.6 0.2 0.2 3.1 3.8 6.3 9.6 2.0 2.5 2.2 9150 84Comparative 1.17 0.6 0.2 0.2 0.4 3.2 4.7 7.5 11.8 2.3 1.0 6400 73Example 3 Comparative 1.17 0.6 0.2 0.2 3.2 4.1 9.6 23.4 3.0 5.7 1.3 666072 Example 4 Example 10 1.04 0.8 0.1 0.1 3.1 3.7 7.1 12.0 2.3 3.2 1.711000 84 Example 11 1.04 0.8 0.1 0.1 2.5 3 5.3 8.2 2.1 2.7 2.3 11700 83Example 12 1.04 0.8 0.1 0.1 3.0 3.7 6.6 9.6 2.2 2.6 4.2 10600 83Comparative 1.04 0.8 0.15 — 0.30 4.5 5.8 7.4 19.3 1.6 1 7100 70 Example5

As shown in Table 1, the positive electrode active materials in Examples1 to 12 exhibit good power density and durability as compared withComparative Examples 1 to 5. Among them, in the case where x satisfies0.3≤x<0.6, Examples 1, 3, and 5 show improved power density, and Example4 shows particularly improved power density. In addition, in the casewhere x satisfies x 0.6≤x<0.8, Example 8 shows good power density, andExample 7 shows particularly good power density. In the case where xsatisfies 0.8≤x<0.95. Example 10 shows good power density, and Example11 shows particularly good power density.

A nonaqueous electrolyte secondary battery including an electrode for anonaqueous electrolyte secondary battery using the positive electrodeactive material of the present disclosure has good power density anddurability, and thus is suitable for large-sized power machines, such aselectric vehicles.

It is to be understood that although the present invention has beendescribed with regard to preferred embodiments thereof, various otherembodiments and variants may occur to those skilled in the art, whichare within the scope and spirit of the invention, and such otherembodiments and variants are intended to be covered by the followingclaims.

Although the present disclosure has been described with reference toseveral exemplary embodiments, it is to be understood that the wordsthat have been used are words of description and illustration, ratherthan words of limitation. Changes may be made within the purview of theappended claims, as presently stated and as amended, without departingfrom the scope and spirit of the disclosure in its aspects. Although thedisclosure has been described with reference to particular examples,means, and embodiments, the disclosure may be not intended to be limitedto the particulars disclosed; rather the disclosure extends to allfunctionally equivalent structures, methods, and uses such as are withinthe scope of the appended claims.

One or more examples or embodiments of the disclosure may be referred toherein, individually and/or collectively, by the term “disclosure”merely for convenience and without intending to voluntarily limit thescope of this application to any particular disclosure or inventiveconcept. Moreover, although specific examples and embodiments have beenillustrated and described herein, it should be appreciated that anysubsequent arrangement designed to achieve the same or similar purposemay be substituted for the specific examples or embodiments shown. Thisdisclosure may be intended to cover any and all subsequent adaptationsor variations of various examples and embodiments. Combinations of theabove examples and embodiments, and other examples and embodiments notspecifically described herein, will be apparent to those of skill in theart upon reviewing the description.

In addition, in the foregoing Detailed Description, various features maybe grouped together or described in a single embodiment for the purposeof streamlining the disclosure. This disclosure may not be interpretedas reflecting an intention that the claimed embodiments require morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive subject matter may be directed toless than all of the features of any of the disclosed embodiments. Thus,the following claims are incorporated into the Detailed Description,with each claim standing on its own as defining separately claimedsubject matter.

The above disclosed subject matter shall be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments which fall within thetrue spirit and scope of the present disclosure. Thus, to the maximumextent allowed by law, the scope of the present disclosure may bedetermined by the broadest permissible interpretation of the followingclaims and their equivalents, and shall not be restricted or limited bythe foregoing detailed description.

All publications, patent applications, and technical standards mentionedin this specification are herein incorporated by reference to the sameextent as if each individual publication, patent application, ortechnical standard was specifically and individually indicated to beincorporated by reference.

What is claimed is:
 1. A positive electrode active material for anonaqueous electrolyte secondary battery, comprising particles of alithium-transition metal composite oxide that contains nickel in thecomposition thereof and has a layered structure, the particles having anaverage particle size D_(SEM) based on electron microscopic observationin a range of 1 μm to 7 μm, wherein a ratio D₅₀/D_(SEM) of a 50%particle size D₅₀ in volume-based cumulative particle size distributionto the average particle size based on electron microscopic observationis in a range of 1 to 4, and a ratio D₉₀/D₁₀ of a 90% particle size D₉₀to a 10% particle size D₁₀ in volume-based cumulative particle sizedistribution is 4 or less; and wherein the D_(SEM) is to be determinedas follows: observing an image at a magnification of 1,000 to 10,000using a scanning electron microscope (SEM), selecting 100 particleshaving recognizable outlines, calculating the equivalent sphericaldiameters of the selected particles using an image processing software,and determining the arithmetic average of the obtained equivalentspherical diameters as D_(SEM).
 2. The positive electrode activematerial according to claim 1, wherein the ratio D₅₀/D_(SEM) of the D₅₀to the D_(SEM) is 1 to
 3. 3. The positive electrode active materialaccording to claim 1, wherein the lithium-transition metal compositeoxide has a composition represented by the following formula (1):Li_(p)Ni_(x)Co_(y)M¹ _(Z)O_(2+α)  (1), wherein p, x, y, z, and a satisfy1.0≤p≤1.3, 0.3≤x≤0.95, 0≤y≤0.4, 0≤z≤0.5, x+y+z=1, and −0.1≤α≤0.1, and M¹represents at least one of Mn and Al.
 4. The positive electrode activematerial according to claim 3, wherein 0.3≤x<0.8, and the ratioD₅₀/D_(SEM) of the D₅₀ to the D_(SEM) is in a range of 1 to
 2. 5. Thepositive electrode active material according to claim 3, wherein0.3≤x<0.6, and a disorder of nickel element in the lithium-transitionmetal composite oxide particles determined by X-ray diffractometry is1.5% or less.
 6. The positive electrode active material according toclaim 3, wherein 0.3≤x<0.6, and the ratio D₉₀/D₁₀ of the D₉₀ to the D₁₀is 3 or less.
 7. The positive electrode active material according toclaim 3, wherein 0.3≤x<0.6, and the ratio D₉₀/D₁₀ of the D₉₀ to the D₁₀is 2.5 or less.
 8. The positive electrode active material according toclaim 3, wherein 0.3≤x<0.6, and the D₅₀ is in a range of 1 μm to 5.5 μm.9. The positive electrode active material according to claim 3, wherein0.3≤x<0.6, and the D₅₀ is in a range of 1 μm to 3 μm.
 10. The positiveelectrode active material according to claim 3, wherein, when 0.3≤x<0.6,1.1<p<1.2.
 11. The positive electrode active material according to claim3, wherein 0.6≤x<0.8, and the disorder of elemental nickel in thelithium-transition metal composite oxide particles determined by X-raydiffractometry is 2.0% or less.
 12. The positive electrode activematerial according to claim 3, wherein 0.6≤x<0.8, and the ratio D₉₀/D₁₀of the D₉₀ to the D₁₀ is 2.3 or less.
 13. The positive electrode activematerial according to claim 3, wherein 0.6≤x<0.8, and the D₅₀ is in arange of 1 μm to 5.5 μm.
 14. The positive electrode active materialaccording to claim 3, wherein 0.8≤x≤0.95, and the disorder of elementalnickel determined by X-ray diffractometry is 4.0% or less.
 15. Thepositive electrode active material according to claim 3, wherein0.8≤x≤0.95, and the ratio D₉₀/D₁₀ of the D₉₀ to the D₁₀ is 3 or less.16. The positive electrode active material according to claim 3, wherein0.8≤x≤0.95, and the D₅₀ is in a range of 1 μm to 5.5 μm.
 17. Anelectrode for a nonaqueous electrolyte secondary battery, comprising: acurrent collector; and a positive electrode active material layer thatis disposed on the current collector and contains the positive electrodeactive material according to claim
 1. 18. A nonaqueous electrolytesecondary battery comprising the electrode according to claim 17.